1. Priority Claim
This application claims the benefit of priority from European Patent Application No. 09004056.9, filed Mar. 20, 2009, which is incorporated by reference.
2. Technical Field
This application relates to signal processing and, more particularly, to attenuating noise in an input signal.
3. Related Art
In a variety of situations, signals may be used to transmit information between two communication partners. Many different types of signals may be used to transmit information, including electric signals, radio signals, light signals, and sound signals. A signal may include both wanted signal components and noise components. The wanted signal components carry the information to be transmitted between communication partners, while the noise components may reduce signal quality or otherwise interfere with the intelligibility of the wanted signal components.
In a telephone system, a sound signal from a user maybe transformed at the sender side into an electric signal. The electric signal may be forwarded via electronic components of a telephone network to a receiver. At the receiver, the electric signal may be transformed back by electronic components into a wanted sound signal. If noise is present in the electric signal received at the receiver side, then artifacts may be audible in the resulting sound signal. Various electronic components in a telephone network, such as network access devices (NADs) or network access modules (NAMs), may add noise to the electric signal. The electronic components may generate noise even when no wanted signal component is present. The noise may be noticeable as artifacts to the receiving party, particularly during pauses of the wanted signal.
Some systems use noise gates, squelch functions, or Wiener-type filters to suppress noise. A noise gate may have the property of suppressing all input signals that have levels below a certain threshold, as shown in FIG. 10. In FIG. 10, an input signal with an intensity level below a gate threshold with an absolute value of 0.4 results in an output of level of zero (i.e., no output at all), while an input signal with an intensity level above the gate threshold may pass with unchanged intensity. Some noise suppression approaches may have a negative impact on the wanted signal components of an input signal. Therefore, a need exists for an improved noise attenuation system, which may have less of a negative impact on the wanted signal components of an input signal.